1. Field of the Invention
The present invention relates generally to optical fiber (hereinafter xe2x80x9cfiberxe2x80x9d) and more particularly to a multiple crucible method of making fiber.
2. Technical Background
The most widely known multiple crucible method of drawing fiber is the double crucible method. The double crucible method of making fiber has been known for at least the last two or three decades, and is disclosed for example in Optical Fibers for Transmission, New York John Wiley, pp. 166-178 (Midwinter, 1979).
Much of the early work in the area of drawing multimode fiber by double crucible exploited the natural tendency of the fiber core and cladding to diffuse (mix). This type of fiber is typically characterized as a fiber with a large core relative to the cladding and a less than step function refractive index change at the interface of the core and cladding (hereinafter multimode fiber). Later work in this area was directed toward creating a parabolic index profile in the multimode fiber. This was accomplished by controlling the diffusion between the core and the cladding.
In the case of making single mode fiber from a double crucible, the challenge of limiting diffusion is much greater for at least the reason that the core of a single mode fiber is much smaller than the core of a multimode fiber. Typical core size of a single mode fiber is 3-6 microns. Thus a diffusion depth of 1 micron may affect a significant portion of the core of a single mode fiber.
Prior attempts to limit diffusion in a single mode fiber have been made in the rod-in-tube method of manufacturing fiber. This method requires the use of distinct portions of core and cladding material. The distinct portions of core material are inserted into the cladding material. This assembly is then consolidated and drawn at a high viscosity. This method suffers from interfacial contamination, increased fiber attenuation, and additional thermal histories being imposed on the glass. The application of additional thermal history is especially harmful to types of glasses that are prone to devitrification.
In addition to diffusion, another problem with drawing fiber from a multiple crucible apparatus is the ability to achieve core clad concentricity. Prior uses of a multiple crucible apparatus teach the crucibles in a fixed orientation to each other. Fixing the crucibles creates a geometry when the crucible hardware is setup and it is hoped that this geometry is maintained once the apparatus is heated to an operating temperature. Consistently, the geometry will change and the resulting fiber will not have a concentric core cladding geometry.
Thus, there is a need in the art to be able to quickly adjust the geometry of the core and cladding of the fiber and to draw a fiber with a core aligned concentrically in a cladding.
The present invention relates to a method of making an optical fiber drawn from a multiple crucible apparatus. Preferably one of the crucibles of the multiple crucible apparatus has a tip with an orifice, wherein the orifice has a non-symmetrical radial axis.
One embodiment of the invention includes a method of making an optical fiber from a multiple crucible apparatus. The method includes
(a) documenting the location in space of an alignment element of an orifice of at least one of the crucibles of the multiple crucible apparatus; (b) drawing an optical fiber from the multiple crucible; (c) documenting a location of a first portion of the drawn fiber with respect to a second portion of the drawn fiber, the second portion of the drawn fiber having an orientation element; (d) moving the a crucible containing the raw materials for the first portion of the drawn fiber relative to the crucible having alignment element; and (e) repeating steps (b)-(d) until a location of the first portion comprises a pre-determined location relative to the second portion having the orientation element.
A second embodiment of the invention also includes a method of making an optical fiber from a multiple crucible. The second method includes (a) drawing an optical fiber from a multiple crucible apparatus wherein one of the crucibles of the apparatus has a circumferential orientation element; (b) documenting a location of a first portion of the drawn fiber; (c) moving a location of a second crucible of the apparatus relative to the crucible having the circumferential orientation element; and (d) repeating steps (a)-(c) until the first portion of the fiber is located at a pre-determined location.
A third embodiment of the invention further includes a method of making an optical fiber. The third method includes (a) drawing an optical fiber from a multiple crucible apparatus wherein one of the crucibles of the apparatus has an orifice having a notch; (b) documenting a location of a first portion of the drawn fiber; (c) moving a location of a crucible for the first portion of the fiber of the apparatus relative to the crucible having the notch; and (d) repeating steps (a)-(c) until the core of the fiber is located at a predetermined location.
A fourth embodiment of the invention further includes a method of making an optical fiber. The fourth method includes drawing an optical fiber from a multiple crucible apparatus, wherein one of the crucibles of the apparatus has a non-symmetrical orifice.
The invention also includes an unique optical fiber. The inventive fiber has a core and a cladding surrounding said core, wherein at least one of said core or said cladding comprises an asymmetrical feature.
One advantage that will result from practicing the invention is that a fiber made in accordance with the invention will have an orientation element. The orientation element provides a reference point to orient any section of the fiber, e.g. a core, an interior cladding, or an exterior cladding. The use of the reference point to orient the section of the fiber will reduce the number of crucible geometry adjustments to locate the section of the fiber to a predetermined point of the fiber, e.g. the center of the fiber. The invention may be used to reduce the amount of time and cost associated with draw apparatus reaching a steady state for drawing useable fiber. The orientation element also provides a reference point to determine a positive and negative direction for both the x and y axes for a Cartesian set of reference points interposed on a cross section of the fiber.
Another advantage that will result from practicing the invention is that the core of the fiber can be aligned concentrically to the exterior of the fiber. Furthermore, practicing the invention will result in any two sections, up to all of the sections, of the fiber being concentrically aligned to each other.
All of the above methods include the advantage of being applicable to both soft and hard glasses. The above methods also have in common at least one more advantage, that the methods may be easily incorporated into existing fiber draw equipment.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.